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Tool Talk Discussion Forum

Power distribution loss

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Ted in NE-OH

01-10-2017 18:57:26




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If a generator at a power plant generates a megawatt of power, what percentage gets lost in transmission to the user? Losses in wires transformers etc. Any factual data out there?




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buickanddeere

01-13-2017 09:41:52




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
Quoting Removed, click Modern View to see

AC had the advantage for long distance transport because of high voltage and low current that low cost, simple and reliable transformers allow. Can't transform DC up and down, well not until recently .
At the same voltage on the same transmission lines, DC is more efficient than AC.



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buickanddeere

01-12-2017 07:04:13




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
The cost per Kw hr did not change , the line loss charge was something brand new added to the power bill. A round about rate increase.



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jeffcat

01-11-2017 18:05:24




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
And remember Edison wanted everything DC. Trouble is it goes flat in just a few miles. Tesla and Westinghouse got it right cause you can go hundreds of miles with very little lose. AC is actually power going back and forth like a pump in the wire so it is far more efficient. DC is just going in one direction so by the time it falls out of the end of the wire there is not much left. Kind of a strange way to describe it but is pretty close. Actually the water or plumbing way is how. Think of water hammering in a pipe. Bet there are other ways to describe this.

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MarkB_MI

01-13-2017 02:44:36




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 Re: Power distribution loss in reply to jeffcat, 01-11-2017 18:05:24  
> And remember Edison wanted everything DC. Trouble is it goes flat in just a few miles. Tesla and Westinghouse got it right cause you can go hundreds of miles with very little lose. AC is actually power going back and forth like a pump in the wire so it is far more efficient. DC is just going in one direction so by the time it falls out of the end of the wire there is not much left. Kind of a strange way to describe it but is pretty close. Actually the water or plumbing way is how. Think of water hammering in a pipe. Bet there are other ways to describe this.

Hmm. Why is it then, that DC is used for long distance transmission lines? For distances over 300 miles DC is preferred over AC. DC transmission is more efficient at ALL distances, but the cost of the devices used to convert high-voltage AC to DC and back make DC impractical over short distances.

The advantage of AC is not that it is "power going back and forth like a pump in the wire". The advantage is it can be easily AND CHEAPLY converted to higher voltage and back to lower voltage. AC suffers from a number of losses to which DC is immune.

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buickanddeere

01-11-2017 14:22:17




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
Ontario power consumers have to pay an extra fee on the power bill to cover the line loss.



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centash

01-11-2017 19:47:40




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 Re: Power distribution loss in reply to buickanddeere, 01-11-2017 14:22:17  
Meter reading is multiplied by 1.092. Is this line loss, 9.2 %, or meter inefficiency? Or another Wynne money grab? Ben



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David G

01-12-2017 07:04:09




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 Re: Power distribution loss in reply to centash, 01-11-2017 19:47:40  
The extra 9.02 % are your losses, it can be programmed into the meter onsite, so it does not have to be calculated elsewhere.



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David G

01-11-2017 14:23:41




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 Re: Power distribution loss in reply to buickanddeere, 01-11-2017 14:22:17  
B&D, everyone ends up paying for this whether itemized or not.



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David G

01-11-2017 12:03:02




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
There have been other questions brought up on combustion efficiency, I think that is probably about 50%, give or take, so the line and transformer losses are after that and relatively small.



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pete black

01-11-2017 08:47:05




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
why do you ask questions like this, do you not know that many of us are retired and trying to put the past behind us? i read with renewed interest John T post, difficult to understand when i worked it and more so now since retirement. actually in generating plants there is limited ways to reduce losses. each unit requires critical aux. equipment that is automatically controlled by pressure switches, electrical sensors or float switches. very few manually operated control circuits exists. losses in generating stations are measured differently than on transmission systems or distribution systems. power plants losses are measured by fuel used versus generation output; regardless of fuel. losses on the primary transmission systems are generally fixed. distribution systems are where losses can be controlled somewhat. distribution transformers are the biggest contributor to system losses, purchasing low loss transformers and correctly sizing the transformer to the applicable load is important to reduce losses. good right of way management (tree trimming) is critical as well. each time a tree limb contacts an energized bare conductor, electricity is bled to ground and therefore bypassing the revenues meters. then there are those noncollectable bills that are written off and of course; thief of services. boy are there inventive ways of stealing power. meter tampering, car battery jumper cables, butter knives in the meter clips and the stealing of a neighbors meter to replace theirs. another contributor to losses is an imbalance of loading on a 3 phase 13 kv distribution line. all this being said system losses on distributions within a city's limits typically range in the 6-7 percent. rural areas co-ops, reas typically range in the 9-11 percent. to make this even longer, David G post concerning VARs was interesting also. actually vars (volts, amps reactive) is a critical component of generating electricity. vars are produced by exciting the generator field and over exciting the field increases the voltage output of the generator. as watts output is increased then a stronger field is needed, therefore field excitation is increased. in generation plants there are megawatts and megavars. generator mws/mvars have two control factors, generator amps and field temperature and both have to be controlled within the limits set by the manufacture. the last big blackout to occur in the mid to late eighties was due to lack of var support on the transmission system. privately owned generating plants lowered the mvar output of the generators to reduce generator amps and field temperatures so they could increase the megawatts output; why, megawatts is what passes through the revenue meters and the var support is eaten by the producer and since these where privately owned plants they where focused on revenue. pete black, not an engineer but long since retired.

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John T

01-11-2017 05:21:05




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
Ted, excellent question, like others I couldn't recall any exact figures since I'm so long retired from power distribution engineering, so cruised the internet and read one report (must be true if on internet right lol) that estimated losses in transmission and distribution in 2007 to be 6.5%.

Some reasons are a) When you pass current through a conductor (and all have some resistance and impedance in AC applications) the power losses in heat generated are I Squared R. b) Also a transformer, not being a 100% efficient device, does not pass all the "electrical" energy out that was applied to the input as again some was converted/lost as heat c) (copied and pasted from the internet) "In any alternating current transmission line, the inductance and capacitance of the conductors can be significant. Currents that flow solely in 'reaction' to these properties of the circuit, (which together with the resistance define the impedance) constitute reactive power flow, which transmits no 'real' power to the load. These reactive currents, however, are very real and cause extra heating losses in the transmission circuit. The ratio of 'real' power (transmitted to the load) to 'apparent' power (sum of 'real' and 'reactive') is the power factor. As reactive current increases, the reactive power increases and the power factor decreases. For transmission systems with low power factor, losses are higher than for systems with high power factor. Utilities add capacitor banks, reactors and other components (such as phase-shifting transformers; static VAR compensators; and flexible AC transmission systems, FACTS) throughout the system to compensate for the reactive power flow and reduce the losses in power transmission and stabilize system voltages. These measures are collectively called 'reactive support'."

In our huge Naval Industrial complex the utility delivered us 138,000 volts three phase which we converted to a 12,470 Y, 7200 Volt Three Phase Four Wire overhead distribution system. Due to heavy AC motor and HVAC (inductive) loads we had a lousy Power Factor for which the utility would charge us an expensive power factor penalty grrrrrrrrrrr. Prior to my retirement we were adding power factor correction capacitors which reduced the power factor but we seldom got it completely down to unity one.

On our smaller home and farm applications the use of adequate size conductors can help reduce I Squared R line losses. When possible I prefer using 240 versus 120 volt devices and even three phase if available in a shop.

Good question, hope this helps, but an answer could take books to better explain and I'm long winded enough anyway lol

John T

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David G

01-11-2017 06:38:21




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 Re: Power distribution loss in reply to John T, 01-11-2017 05:21:05  
John,

Most industrials pay for apparent power (kVA), so power factor is in there.

Power factor correction is always encouraged due to the utility not having to provide the imaginary power, (VAR), but I think the stiff penalties start at about 95%. It is also important to remember that capacitors appear as a dead short when generators are started, so must be disconnected in the case of a power failure. The use of VFD's now has really helped the power factor issue, they appear as unity, or even a little bit leading to the utility.

I have seen the power factor down in the low 80s in rural Iowa when grain dryers and elevators are working hard

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part time pete

01-11-2017 04:49:46




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
Oil fired plants have parasitic losses too. I worked at a dual fuel plant back in the day - a 1300 megawatt plant that could run on natural gas or heavy oil. If I remember right, it took about 60 megawatts to run the pumps, fans, heaters etc. Pete



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David G

01-11-2017 06:41:13




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 Re: Power distribution loss in reply to part time pete, 01-11-2017 04:49:46  
That is termed station power, or the electricity required to generate, it includes pumps, fans and excitation power. Generation is sold as net or gross, net generation is the generation minus the station power. It is a good deal if you can sell gross generation and make the downstream pay for the station power.



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Geo-TH,In

01-11-2017 04:39:47




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
I think if you look at how much energy it takes to make electricity you may see a substantial loss. Most coal fired plants generate more heat energy than electrical energy. Some say it requires a lot of energy just to crush the coal, run the pumps and fans. I don't have percentages of energy in each catagory, but I'm guessing the actual electrical energy sold will be surprisely low.



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TN 2N

01-10-2017 20:26:01




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
I work for a Local Power company in Tennessee. We serve about 20,000 customers and cover about 600 square miles. We buy power at 161,000 volts. From the purchase point to the customers meters, our loss runs between 5 and 5.5%



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David G

01-10-2017 19:16:53




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
You also have to remember that there are watts and VARs, VAR's are imaginary watts, but have to be generated.



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David G

01-10-2017 19:15:41




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 Re: Power distribution loss in reply to Ted in NE-OH, 01-10-2017 18:57:26  
Yes, there are tables, and it is per line and per transformer, must be summed.

I am trying to remember, but I think it is estimated to be about 5%.



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Billy Shafer

01-10-2017 19:21:47




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 Re: Power distribution loss in reply to David G, 01-10-2017 19:15:41  
There are allot of factors involved but I think 5% is correct.



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David G

01-10-2017 19:31:10




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 Re: Power distribution loss in reply to Billy Shafer, 01-10-2017 19:21:47  
I did a bunch of these calculations when I was in the utility metering, but just cannot remember.



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Billy Shafer

01-10-2017 20:02:16




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 Re: Power distribution loss in reply to David G, 01-10-2017 19:31:10  
I retired from power systems ten years ago. Used to know all that stuff.Amazing what you can forget if you don't use it. Then it pops in your head at 2 in the morning.



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David G

01-10-2017 20:05:17




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 Re: Power distribution loss in reply to Billy Shafer, 01-10-2017 20:02:16  
It seems to comes back if I start conversing and sneak up on it, but just does not seem to pop right out like it did when I was younger.



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